proportioning valve

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by backlash, Nov 27, 2001.

  1. backlash

    backlash 1/2 ton status

    Oct 21, 2000
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    Northern, VA.
    What's the purpose of a proportioning valve? Even pressure, right to left? Front to back? Or all wheels at the same time?

    Having problems with front end pulling on dry pavement and Locking up in front when wet.

    Thought I'd try another approach.

  2. 55Willy

    55Willy 3/4 ton status

    Jun 2, 2001
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    Keizer, Or
    AFAIK the P-valve work in front to rear brake pressure. As far as your truck pulling to one side, you may want to rebleed your brakes.
    Does it also pull to one side when stopping?
    Or your p-valve maybe bad, I have never heard of one going sour.

    <font color=red>Life is like a mud hole:</font color=red><font color=blue>
    When the S#!T gets deep, you have to keep moving and friends can always pull you out</font color=blue>
    55 Willy's
  3. Leadfoot

    Leadfoot 1/2 ton status Premium Member

    Nov 28, 2000
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    Western Massachusetts
    When was the last time the calipers were replaced? I don't think pulling left or right is a prop. valve induced condition. The prop. valve proportions the hydraulic pressures from the front discs to the rear drums (on a typical K5 setup). I would bleed all the brakes (good thing to do to flush old fluid out regardless of the cause of the pulling). Then I would consider doing a brake job on the front turning/replacing the rotors (depending on wear) and putting new pads AND calipers on. As calipers get old, they sometimes loose their effectiveness or one "grabs" better than the other (or sticks) causing the vehicle to pull and/or lockup in slippery conditions (both can be dangerous). Another thing to look for is grease and/or oil soaked into the pads (this can also cause the stated conditions). When this happens you need to replace them as well as cleaning the rotor surface with brake cleaner (and turning/replacing if necessary). Also you need to look at the wheel bearing seals. If there is grease on the rotor it is highly likely that it is coming from the seal at the back of the rotor. This means grease is getting past the seal, which means A.) your bearings are loosing grease. and B.) that water and contaminants can make their way to the bearings (both conditions are not good). If this is the case you will also need to clean, inspect, and repack/replace the bearings as needed as well as install new seals.
    If the calipers are original and or haven't been replaced in awhile I would "suggest" replacing at least the fluid (by bleeding), flex lines, calipers, and pads (then replace the rotors if they cannot be turned down anymore or are "untrue"). This is cheap insurance (brakes and steering are two safety items you want in perfect condition). Just my $.02
    Hope this helps.

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  4. dyeager535

    dyeager535 1 ton status Premium Member

    Dec 13, 2000
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    Roy WA
    Prop. valve is blamed way too often because people don't know what it does. Heres some decent reading.
    Why insist on counting when the ring gear has the tooth counts stamped in?
  5. Blue85

    Blue85 Troll Premium Member

    Jul 26, 2000
    Likes Received:
    Grand Rapids area
    The "proportioning valve" is really a combo valve that does three things
    1) Proportion the brake line pressure from front to rear
    2) Prevent the front pads from engaging until the rear shoes have started to engage
    3) give an indication if there is low pressure in one of the circuits (drive the "brake" light on the dash)

    The left and right front brake lines come from exactly the same feed. The only way the prop valve can cause pulling in the front is if there is a foreign object lodged in it.

    In my experience, pulling is almost always due to differences in the calipers. Either one is sticking and not not allowing the piston to move freely or one is not sliding as easily on the mounting bolts.

    Pull off the calipers and look for damaged seals. A bad seal lets moisture in which casues rust and hanging up. Then take out the little sleeves that the calipers slide on, clean up the sleeves and the bolts completely, then coat it all with some white lithium grease and put it all back together. With the piston retractded into the bore (i.e. slop between the pads and the rotor) the caliper should slide in and out by hand.

    <font color=green>Oh man, 4:10's are sure better than 3.08's!</font color=green>

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